Prior Cryopreservation of Ex Vivo-Expanded Cord Blood Cells Is Not Detrimental to Engraftment as Measured in the NOD-SCID Mouse Model

Abstract

Cytokine-mediated expansion has been proposed and successfully used to facilitate engraftment post transplantation. This study examined whether cryopreservation following expansion has a detrimental effect on the ability of cells to engraft, using the NOD-SCID mouse model. Cord blood (CB) CD34⁺ cells were incubated for 7 days with stem cell factor (SCF), flt-3 ligand (FL), and megakaryocyte growth and development factor (MGDF). Expanded CD34⁺ cells were transplanted into NOD-SCID mice either fresh or following cryopreservation and thawing. After thawing, recovery of nucleated cells was 94%, of CD34 cells was 63%, and of day-14 progenitors was 17%. The loss of day-14 progenitor cells among the thawed expanded cells did not influence the kinetics of human engraftment in the mouse. Bone marrow (BM) of mice transplanted with thawed expanded CD34⁺ cells (14 ± 3.9%) showed significantly higher levels of human engraftment than mice transplanted with fresh expanded CD34⁺ cells (1.5 ± 0.5%, p = 0.0064). Thawed expanded CD34⁺ cells had significantly higher SCID Engrafting Potential (SEP) than freshly expanded CD34⁺ cells (p < 0.001). Results suggest that prior cryopreservation does not prevent expanded cells engrafting in NOD-SCID mice.